Roll crushing apparatus have long been used as an initial step in an ore comminution process. Typically, the function of the roll crushing apparatus is to initially break up the large ore fragments into smaller fragments, which are thereafter further comminuted by other processes.
Roll crushing apparatus typically consists of two roll crushers mounted for rotation about parallel axes. The roll crushers are disposed with their outer circumferential crushing surfaces spaced apart an amount corresponding to the size of the desired output product. Generally, one of the roll crushers is rotatably driven about a stationary axis, with the other freely rotatable on a mounting which is spring biased toward the first.
A roll crusher design which has enjoyed substantial commercial success utilizes a hub upon which a replaceable, annular roll member is mounted. The hub has a circumferential surface that defines a shallow, concave V, one tapered surface of which is defined by a removable clamping ring. The inner circumference of the roll member has a complementing, slightly projecting V-shaped surface. With the clamping ring removed, the roll member is placed on the hub. The clamping ring is then mounted, which exerts some degree of wedging force against the roll member. However, this force is not sufficient to restrain relative rotational movement between the roll member and hub during operation. Consequently, the roll member is heat shrunk on through the use of a furnace.
Several problems result from this structural configuration. First, because heat shrinking is required, the roll member cannot be made from material having a high Brinnell hardness or which offers good resistance to abrasion. Extremely hard, abrasion resistant materials are preferable for crushing operations, but they are extremely brittle and cannot withstand the internal stress forces created during the heat shrinking process. As a result, the roll member for this type of prior art device has been made from material which is of only moderate hardness.
Second, for successful heat shrinking to take place, the V-shaped engaging surfaces of the roll member and hub must be machined to fairly close tolerances, which is difficult and time consuming for an article of this nature. Typically, the roll member itself has an outside diameter of four feet and weighs approximately two tons.
Thirdly, replacement of a worn roll member, which is frequently necessary because of its moderate hardness, is difficult, time consuming and somewhat dangerous due to the extreme heat necessary for proper heat shrinking to occur. Often times, the initial steps of removing the clamping ring and roll member themselves are extremely difficult because of the heat shrunk, close tolerance fit, coupled with peening of the roll member that occurs during the crushing process.
The need for frequent replacement of worn roll members is a negative economic factor. Ore processing plants are often run on a 24 hour continuous basis. The relatively rapid wear of the roll member, which necessitates replacement of the entire component, coupled with the downtime necessary for its replacement, results in a very costly operation.
A number of prior art devices have employed roll members formed from material which is harder than the supporting hub, and which requires less frequent replacement. However, each has employed a structural approach which is either unwieldy from the standpoint of roll member replacement, requires the roll member to be made from a plurality of segments, or does not insure that the newly replaced roll member will be centered and balanced on the hub.